Do you find that humidity effects temps in your UDS?

I've got a UDS that I've used multiple times. With all the vents open it has gotten to 300 degrees in the past. This week, however, I smoked two butts and the smoker never got above 219 and mostly sat around 190. I used multiple thermometers (6 in total) so I'm pretty sure that wasn't the problem. It was, however, extremely humid with thundershowers before I started. I also keep my lump in the basement where it's so humid the walls occasionally sweat. Could this have been the reason my temps were so low?

There wasn't much else different about this smoke except that it was the first time I cooked two butts instead of one. The lump was the same (RO) and there was nothing blocking the vents. One thing I noticed that may (or may not) be related is that the drum seemed hotter than usual. Any ideas?

Thanks guys. A few follow-up questions:

1) I assume you're saying the lump got damp while being stored in the basement, yes? Also, the humidity at burn-time had little to do with it.

2) Where/how do you store your lump? I don't have many options other than to store them in the basement.

3) Are my current bags of lump redeemable? I.e. if I store them in a dryer place will they eventually dry out?